Silverlight 1.0 focused largely on rich media — primarily Web-based video — and used JavaScript as its programming model. It was, to a large extent, Microsoft’s reaction to the rapid proliferation of Flash video in Web-based advertising and on popular sites like YouTube and MySpace.

Silverlight 2 is targeted at “rich Internet applications” (RIAs) and allows development in any .NET language including Visual Basic, C#, JavaScript and others.

With version 2 Silverlight is poised to more broadly complete with Adobe’s Flash platform and the kinds of RIAs people are building with tools like Adobe’s Flex. Silverlight 2 will include controls for forms, layout management, data manipulation, and much more. See Guthrie’s post for the details.

One key fact — long presumed but good to have confirmed — is that “Silverlight 2 does not require the .NET Framework to be installed on a computer in order to run. The Silverlight setup download includes everything necessary to enable all the [listed] features … on a vanilla Mac OSX or Windows machine.”

And one long-awaited tidbit regarding the size of Silverlight 2: “The Beta1 release of Silverlight 2 is 4.3MB.”

Silverlight 2 is, in Guthrie’s words, “a cross-platform, cross-browser version of the .NET Framework, and enables a rich .NET development platform that runs in the browser” with “.NET APIs [that] are a compatible subset of the full .NET Framework.”

And this is why the file size data is so interesting. Based on a quick survey, it looks like the redistributable packages of previous versions of the .NET framework for x86 processors are as follows: